Invertebrates and fish hear sounds at low frequency, while cetaceans (dolphins and whales) can hear very high frequencies, up to 200kHz and also use active sonar to detect objects, including prey. Sound travels 4.5 times faster through water than through air, meaning many marine organisms have evolved to rely on sounds to provide important cues to navigate, forage for food, avoid predators and enable communication. “Despite their attempts to compensate, despite being highly motivated and the fact that they know this cooperative task so well, the noise still impaired their ability to successfully coordinate,” said Sørensen. The highest noise levels were comparable with what are sometimes experienced in marine environments as a result of shipping and drilling. The dolphins also changed their body language, reorienting themselves to face each other more frequently at higher noise levels and swimming across the lagoon to be closer to each other. From the lowest to highest levels of noise, the dolphins’ success rate dropped from 85% to 62.5%, according to the research. Nevertheless, they could not entirely compensate. When increasing levels of noise were played from an underwater speaker, both dolphins compensated by changing the volume and length of their calls to coordinate the button press. This meant that the dolphins had to rely solely on vocal communication to coordinate the button press. They were released from a starting point during each trial, and in some trials, one of the dolphins was held back for five to 10 seconds. The dolphins were required to work together to both press their own underwater button placed at either end of a lagoon within one second of each other – a task that some humans would struggle to coordinate. The latest study involved a pair of dolphins, Delta and Reese, and looked at how their ability to cooperate was affected by background noise. So noise generated from human activity such as drilling and shipping has a potentially harmful impact on the health of marine populations. Dolphins are social, intelligent animals, relying on clicks and whistles to communicate and using echolocation to hunt and navigate.
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